Define Yankee, please. My definition is north of the Mason Dixon, and east of the Mississippi.
I guess the Mason-Dixon line is the "official" designation but the popular frame of reference is the states that were in the Confederacy which excludes Maryland.
Using points east of the river leaves out Louisiana, Arkansas and Texas which are technically part of the South, though I tend to think of Texas as it's own little corner of the world.
Oklahoma, or the Indian Nations during the war, was the only official ally the South had and was considered part of the South, but for all other purposes I consider it mid-west.
I have lived on the west coast all my life and I don't consider myself either one. Yankees are very distinct from the folks out west.
To Southerners, anyone not from the South is technically Yankee...sorry.